1. Field of the Invention
This invention relates to a picture display method and apparatus for displaying a picture by spatially modulating the light outgoing from a light source and projecting the modulated light.
2. Description of the Related Art
Among picture display apparatus used for the purpose of appreciating a picture, there is a projection type picture display apparatus in which the light outgoing from a light source is spatially modulated by a picture display light valve for projection on a screen. This projection type picture display apparatus is classified into a front side projection type in which the picture is projected from the front side, such as a screen, and a back side projection type in which the picture is projected from the back side of the screen. As this projection type picture display apparatus, there is known such apparatus in which a white light source, including a discharge type xenon lamp, a metal halide lamp or a heat light emission type halogen lamp, is used as a light source, and a liquid crystal light valve is used as a picture display light valve.
FIG. 1 shows an illustrative structure of a conventional projection type picture display device. This projection type picture display device includes a lamp 201 emitting a white light beam, a UV-IR cutting filter, not shown, for cutting the ultraviolet light (UV light) and infrared light (IR light) of the light radiated from the lamp 201, and a lens 202 for condensing the light passed through the UV-IR cutting filter. This projection type picture display device also includes a red color separating mirror 203 reflecting only the red wavelength component of the light condensed by the lens 202 and transmitting other wavelength components, and a green color separating mirror 204 for reflecting only the green wavelength component passed through the red color separating mirror 203 and transmitting other wavelength components. The projection type picture display device also includes a blue color separating mirror 205 for reflecting only the blue wavelength component passed through the green color separating mirror 204 and transmitting other wavelength components. As the lamp 201, a white light source, such as a xenon lamp, a metal halide lamp or a halogen lamp, is used. As the mirrors 203 to 205, dichroic mirrors are used.
The projection type picture display device also includes a cubic-shaped synthesis prism 210, arranged for causing the green light reflected by the green color separating mirror 204 to fall on a surface 210G of the synthesis prism 210, and a reflection mirror 206 for causing the red light reflected by the red color separating mirror 203 to fall on a surface 210R of the synthesis prism perpendicular to the surface 210G. The projection type picture display device also includes a reflection mirror 207 for reflecting the blue light reflected by the blue color separating mirror 205 so as to fall on a surface 210B of the synthesis prism parallel to the surface 210R of the synthesis prism 210.
The projection type picture display device also includes a red picture display light valve 211R arranged between the reflection mirror 206 and the surface 210R of the synthesis prism 210, and a green picture display light valve 211G arranged between the green color separating mirror 204 and the surface 210B of the synthesis prism 210. The projection type picture display device also includes a blue picture display light valve 211B arranged between the reflection mirror 207 and the surface 210B of the synthesis prism 210, and a projection lens 212 arranged facing a surface 210A parallel to the surface 210G of the synthesis prism 210. The light valves 211R, 211G and 211B may, for example, be rectangular in shape. The light valves 211R, 211G and 211B are adapted for being driven on the basis of red picture signals, green picture signals and blue picture signals, respectively.
The projection type picture display device also includes a red field lens 212R arranged between the reflection mirror 206 and the red picture display light valve 211R, and a green field lens 212G arranged between the green color separating mirror 204 and the green picture display light valve 211G. The projection type picture display device also includes a blue field lens 212B arranged between the reflection mirror 207 and the blue picture display light valve 211B, and an optical path length adjustment lens 213 arranged between the blue color separating mirror 204 and the blue color reflection mirror 205. The projection type picture display device also includes an optical path length adjustment lens 214 arranged between the blue color separating mirror 205 and the reflection mirror 207.
The synthesis prism includes a reflecting mirror 210r for reflecting only the red light incident from the surface 210R towards the surface 210R, and a reflecting surface 210B for reflecting only the blue light incident from the surface 210B towards the surface 210A.
The above-mentioned components of the projection type picture display apparatus are held by a suitable holder and installed in this state in a casing 214.
In the projection type picture display apparatus, shown in FIG. 1, the white light radiated from the lamp 201 is freed by the UV-IR cutting filter of redundant wavelength light beams, that is the UV and IR light beams, and condensed by the lens 202 so as to fall on the red color separating mirror 203. Of the light incident on the red color separating mirror 203, the red light is reflected by the red color separating mirror 203. The reflected red light is further reflected by the reflection mirror 206 to pass via red field lens 212R through the red picture display light valve 211R and is spatially modulated based on red picture signals so as to fall on the synthesis prism 210.
Of the light incident on the red color separating mirror 203, the light other than the red light is transmitted through the red color separating mirror 203 to fall on the green color separating mirror 204. Of the light incident on the green color separating mirror 204, the green light is reflected by the green color separating mirror 204 and transmitted via green field lens 212G through the green picture display light valve 211G and is spatially modulated based on red picture signals to fall on the synthesis prism 210.
Of the light incident on the green color separating mirror 204, the light other than the green light is transmitted through the green color separating mirror 204 to fall on the blue color separating mirror 205. Of the light incident on the blue color separating mirror 205, the blue light is reflected by the blue color separating mirror 205, reflected by the reflection mirror 207 through the optical path length adjustment lens 214 and transmitted via blue field lens 212B through the blue picture display light valve 211B and is spatially modulated based on blue picture signals to fall on the synthesis prism 210.
The light beams of respective colors, modulated by the light valves 211R, 211G and 211B, are synthesized by the synthesis prism 210 so as to be then radiated from the surface 210A to fall on the projection prism 212. The light beams are then projected to an enlarged scale on a transmission or reflection projection type picture display apparatus type screen 213.
The above-described conventional projection type picture display apparatus has a defect that, since the white light source (lamp), such as xenon lamp, metal halide lamp or halogen lamp, used as a light source, generally undergoes significant chronological changes, and is of short service life, the picture tends to become dark, while the lamp tends to be used up, such that the displayed picture tends to become dark or the lamp has to be exchanged during display of the picture.
On the other hand, the light beam radiated from the white light source used in the conventional projection type picture display apparatus is usually of a circular cross-section, whereas the picture display light valve is usually of an elongated shape. Thus, in the conventional projection type picture display apparatus, the diameter of the light beam radiated on the picture display light valve is set so as to be longer than the length of a diagonal of the light valve in order to illuminate the light from the white light source uniformly on the picture display light valve. The result is that much light is wasted to lower the utilization efficiency of light from the light source.
Moreover, the conventional projection type picture display apparatus has a defect that, because of the low utilization efficiency of light from the light source, a brighter light source needs to be used for obtaining the necessary brightness, and a defect that, since a larger light source needs to be used for realizing the necessary brightness, it becomes necessary to reduce the size of the projection type picture display apparatus.
In the projection type picture display apparatus, there are occasions wherein a picture of a given aspect ratio is switched to one of another aspect ratio, such as in the case of switching between display of a picture with the aspect ratio of 3:4 of the NTSC (National Television System Commission) and display of a picture with the aspect ratio of 9:16 of the hi-vision system. In this case, the shape and the area of an area actually used in the picture display light valve are changed depending on the aspect ratio. With the conventional projection type picture display apparatus, if the shape and the area of an area actually used in the picture display light valve are changed, the light volume effectively used in the projection type picture display apparatus is also changed, as a result of which the brightness of the projected picture is also changed.
With the conventional projection type picture display apparatus, the outgoing light beam of the white light source is color-separated by color separation means, such as a dichroic mirror, and the resulting separated light beams are illuminated on picture display light valves associated with the respective color signals. The result is that the wavelength distribution of the separated colors depends on the wavelength distribution of the outgoing light of the original white light source to make difficult optimum color reproduction.
Moreover, in the white light source used in the conventional projection type picture display apparatus, brightness modulation is generally not possible or only narrow in brightness adjustment range, with the response time of brightness modulation being longer, such that, in the conventional projection type picture display apparatus, the displayed picture cannot be adjusted in brightness or can be adjusted only in a narrow range.
Also, if, in the conventional projection type picture display apparatus, the radiated light of the white light source is color-separated by, for example, a dichroic mirror so as to be illuminated on picture display light valves associated with respective color signals, it is difficult to adjust brightness of the light from one color to another. Further, in the conventional projection type picture display apparatus of the type in which color filters are provided in the picture display light valves for color separation, color adjustment can be done only by adjusting the picture signals associated with respective colors or by changing color filters used. Thus, with the conventional projection type picture display apparatus, fine color adjustment is difficult or can be realized only in a narrow range.